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All topics
Year 10
Trigonometry
Definition
Trigonometry connects the angles of a right-angled triangle to the ratios of its sides. Sine, cosine and tangent (sin, cos, tan) each compare a different pair of sides, so one angle and one side are enough to find the rest.
Why Do I Have to Learn This?
Trigonometry links angles to lengths in triangles. Engineers, pilots and animators use it to work out heights and distances.
Key Rules:
- 1. Label the sides first: hypotenuse (longest), opposite (facing the angle), adjacent (next to it).
- 2. SOH CAH TOA picks the ratio: sin = opp/hyp, cos = adj/hyp, tan = opp/adj.
- 3. Finding an angle uses the inverse function (sin⁻¹, cos⁻¹, tan⁻¹).
Remember:
- •Common slip: mixing up opposite and adjacent, always label from the angle you are using.
- •The hypotenuse is always opposite the right angle and is never the opposite or adjacent.
- •Check your calculator is in degrees, not radians.
Cosine
One of the three trigonometric ratios. In a right-angled triangle, cos of an angle = adjacent ÷ hypotenuse.
cos 60° = 0.5, so when the hypotenuse is 10 cm the adjacent side is 5 cm.
Animated Example:
3² + 4² = 25, so c = 5
Free Trigonometry Worksheet
Download free worksheets and practise today.
Every download has a fresh set of questions.
Let’s Practise the Concept
Step 1 of 3
Put them in order
Tap the numbers from smallest to largest.
In order so far: nothing yet